Method and apparatus for rapid search distance measuring equipment



July 15, 1969 METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE Filed July21. 1967 POWER TO EACH SECTION MODULATOR POWER SUPPLY J. L. AKER3,456,257

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METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT FiledJuly 21, 196? 1'7 Sheets-Sheet 1 INVENTOR John L flker' METHOD AN!)APPARATUS FOR HAIH) SI IAINJH DISTANCE MEASUIHNG EQUIPMENT INPUT i i EWAVEFORM o l 1 7' l l I I l g l I i I srceamo I JUNCTION o I I 1 COLLECTQ Q F TRIGGESRQD 0, UNSATURATED Ia (MADE REAUY/ COLLECTORO DUE TO Q20/l\ I Q g big [TRIGGER i 20 Q T 9 THROUGH 1 COLLECTORO "b? c R2 I OFFSWITCHIN i Q 30 SATURATED G COLLECTORO QTPYfTFQ SATURATED i n TRIGGERQ40 THROUGH CR44 COLLEC TORO CARRY oufrPur COLLECTOR o A INVENTOR z g15. Jar/7n L flkel' July 15, 1969 J. L. AKER 3,456,257

METHOD AND APPARATUS FOR RAPLI) SHAHUH DISTANCE MEASURING EQUIPMENTFiled July 21, 1967 17 Sheets-Sheet 1' F INPUT Q b 921;

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METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT FiledJuly 21, 1967 1'7 Sheets-Sheet 10 comuowe COUNT TRKSGER COUNT LOOPBIQUINARY July 15, 1969 J. L, AKER 3,456,257

METHOD AND APPARATUS FOR RAPID SlilAHCH DISTANCE MEASURING EQUIPMENTFiled July 21, 1967 17 Sheets-Sheet l1 TRANSMITTER SM TT R FIRESINTE'RROGATION L ..........L =E%R l MARP'QER PULSE MARKER PULSE IOOnmCOUNTERS COUNTERS O- +-2.5M5:- F RUNNING I i I l R Y I R Y R RECEWED/EPL EPL :/N0 REPLY i EPLY Ill: H |l|| i l I +I4v I I I COLLECTOR s R sR s I *BV :DISCHARGES THROUGH CHARGE THROUGH /R637 I @609 EMITTER R,638F'RES FROM FIG.|7 4 3 2 O READOUT COMMON E" TRIGGER V r r INPUT CARRY jOUTPUT INVENTOR 3T 1/ .10/7/7 L. Hker CARRY OUTPUT July 15, 1969 J. L.AKER 3,456,257

METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT FiledJuly 21, 1967 17 Sheets-Sheet l2 EEHDOUT INHIBIT" CLOCK 6475 T MEMORYnun/0 HI 0/ 624 T/ON PULSE nun/0 EMORY CARRY "ONE" TRHCK ZERO RESET A AKER /NVE'NTOR John L. Aker July 15, 1969 J. L. AKER 3,456,257

METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT FiledJuly 21, 196! 17 Sheets-Sheet w +6v ow unnaofzem IN ITIATION CKT BDINVENT OR 1 19. 21. John L. Hken y 5, 1969 J. L. AKER 3,456,257

METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT FiledJuly 21, 196'? 1'7 Sheets-Sheet 14 MARKER MARKER INV.

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FIGS FIG. 3 INVENTOR John L. Aker' FIG. 4 FIG. 6 FIG 7 July 15, 1969Filed July 21, 1967 IN TERROGA 770M J. L. AKER 3,456,257 METHOD ANDAPPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENT l7 Sheets-Sheet17 i RANDOM Pow 4r REPLY PuLsss a 4 AND /2 r/L55 A r 20 m/LEs mm" PUL5E5{VIDEO l "J r 1 H g i MARKER nrzsna MILES WAR/(5Q m- N0 za gss wmmv r I5Mlckosecouos or MAR-KER WEMORY f B TRIGGER M I960 PULSES -l -.1 2000PUL5E5 FIRST INTERROGATION R4 NUOM PUL5E RANDOM PuLsE RA NUOM PULSE A TBELOV 25x0 MILES A r /5' M/LE5 m5 MIL Es supenssorm RIEPLY {FL-cam: 51050 MARKER A r 4 MILE5 MARKER. 111/ N0 REPLIES WITHIN MICROSECONDS 0FMARKER H llmlllhlmh *[9/0 SECOND I TERROGA T/ON :REQEWEQ: RANDOM PULSERANDOM Put- E REPLY PULSE 13 /050 1 1 (47/29 M/LE5 I/A r M lLEs I gmuaom REPLY m Rmvqr MARKER puma. Mnkxek. [TENTATIVE] 1 AT 1.9 M/Les{MEMORY} L00 -0H7 grmaazn 2000 mass 1 THIRD INTERROGA no I i g i ON THEFOURTH THROUGH 5VENTH INTERROGA nous THE MARKER w/u. REM/N A r mom/LE:we m 7746 occumeuce OFA RANDOM REPLY w/mnv I 3 THE RANGE an r5 ON THErmno IHTERROGA r/orm: LASTDELAY GENERATOR S (NH/BITS MA RKER Any/was FDRFOUR mrzmaoan m WHEN 721/5 HAPPENS l I g RANDOM ,(REPLY PuLsE germ/ LLSES J nrzo MILES l I VIDEO Mim/ ER Puma @RKBQ. AT /3 MILES i 1930.lmnmlh lh Ithmullahhfiinlm.1Mun "H/L5E2 I 5 E/GHT INTERROGATIO I i lREPLY PULSE gscflvio: 1 l 1 AT zom/Lss I VIDEO I REPLY m RANGE GA TEMARKER 'LMARKERJ' mum rlve rh Ar 20 MILES LOCK- 0N1 -2000PUL$E5 LOCK-'ONIN TERROGA T/0Ns INVENTOR L 1/0/7/7 L. flker United States Patent 3 456257 METHOD AND APPARATUS FOR RAPID SEARCH DISTANCE MEASURING EQUIPMENTJohn L. Aker, Olathe, Kans., assignor to King Radio Corporation, Olathe,Kans., a corporation of Kansas Filed July 21, 1967, Ser. No. 655,182Int. Cl. G01s 9/02 US. Cl. 343-73 14 Claims ABSTRACT OF THE DISCLOSURE ADME of the type adapted to transmit interrogation pulses and to receivereplies from a ground station transponder, said replies being both inresponse to said transmitted interrogation pulses and in response toother interrogation pulses from other DME units operating Background andbrief description of the invention This invention is an improvement ofthe invention disclosed in my patent application Ser. No. 574,701, filedAug. 24, 1966, and entitled, Method and Apparatus for DigitallyMeasuring Distance now Patent No. 3,412,400. It relates todistance-ground speed measuring equipment and :more particularly todigitally operated equipment which includes a rapid search mode ofoperation. This equipment, commonly referred to as a DME, functions bymeasuring the length of time between transmissions of a radio signal toa preselected VOR/DME station and reception of a reply signal. Thedistance may then be indicated in nautical miles on a range/speed/ timeto station indicator.

Distance, measured on a slant, from air to ground, is commonly referredto as slant-range distance and should not be confused with the actualground distance. The difference between ground distances is smallest atlow altitude and long range. These differences may vary considerablywhen in close proximity to a VOR/DME facility, however, if the range isthree times the altitude or greater, this error is generally negligiblefrom the pilots point of view.

For further background information, distance measuring equipment is anoutgrowth of radar ranging techniques, whereby a distance is determinedby measuring the round-trip time of travel of radio pulse signalsbetween the two points in question. In DME (distance measuringequipment) systems, a direct reading indicator is used to displaydistance rather than the visual use of a cathode ray tube, as ispeculiar to radar systems. Also, instead of depending on fragilereflections or echoes for the return trip of the pulses, a transponderor beacon is used to produce artificial echoes. These artificialresponses are stronger and their radio channels positively identify thesource of the echo and hence the geographic location of the echoingpoint.

The airborne transmitter repeatedly sends out very short, widely spacedinterrogation pulses. These are picked up by the ground beacon receiver,'whose output triggers the associated transmitter into sending out replypulses on a diflerent channel. These replies are finally picked up bythe airborne receiver. Timing circuits automatically measure the roundtrip travel time, or interval between interrogation and reply pulses,and convert this time into electrical signals which operate the distanceindicator.

3,456,257 Patented July 15, 1969 ice In system operation, a given groundbeacon (transponder) will be interrogated by a number of aircraft whichare Within range and which have tuned to its channel. The ground beaconwill then reply to all interrogations, and each airplane will receivethe sum total of replies to all airplanes. To permit interference-freeoperation under such normal conditions, it is .arranged that eachaircrafts interrogation pulse occur at a rate that is intentionallypermitted to jitter or vary (within certain limits) in an irregular orrandom manner. The jitter" effect is obtained essentially 'by permittinga randomly modulated timing circuit to exercise gross control over theinterrogation rate. In order to determine which ones among the replypulses received on a given aircraft are replies to that aircrafts owninterrogation pulse, a unique search process entirely automatic in itsoperation, is employed by the present invention.

The search operating principle is to locate the proper reply pulse byfinding the one fixed time delay, measured always from the DMEs ownprevious interrogation pulse, at which a reply pulse is repeatedlyreceived. Because interrogation pulses from other air-craft arenon-synchronous or random with respect to the given .aircraftsinterrogation pulse, reply pulses corresponding to such foreigninterrogations will not be received regularly at one fixed (or slowlychanging) time delay, on the given aircraft. This search mode ofoperation is completed in approximately .01 of time required by thesearching method described in my Patent No. 3,412,400, supra.

The DME, in the search mode of operation, searches automatically eachtime the airborne set is initially tuned to a new ground-beacon channelor if there is some major interruption in the radio signals. The systemscans, progressively, each received reply by means of a sliding rangegate or time slot which quickly tests each time slot position for thenumber of successive reply pulses received within a certain uniformchecking period. If no replies or only sporadic replies are received,the time slot is immediately advanced to the next received reply, and soon. When, at some particular time interval, safe evidence of recurrentreplies is detected (by a unique counting process) the search iscompleted and stopped, since this condition is fulfilled only byreception of a desired number of reply pulses. Those pulses are the onlyones which are always received with the same time relationship to thegiven airplanes own randomly jittered interrogation pulses.

Thereafter, the unit locks onto the proper pulses and transfers over totrack operation. The term track is used to indicate that the delaysetting of the timing circuits automatically and continuously followsany normal variation in the time delay of the proper reply pulses. Suchvariations will occur if the airplanes distance is actually changing asa result of its flight path, but are necessarily very small because ofthe relationship between interrogation rates and actual airplane speeds.This relationship will be discussed in greater detail infra.

All the time that the DME is locked onto the proper reply pulses duringthe tracking process, the time delay setting on the range-gate or timeaperture is a proportionate measure of the airplanes distance from theground beacon (approximately 12 microseconds roundtrip travel time pernautical mile). The circuitry that varies the time delay of the timeslot is used to position corresponding numerical, or meter indicators ofsuitable design, on a distance readout by means of electrical controlsignals.

An object of the invention is to provide a new and improved, fasteracting, more versatile DME.

Another object of the invention is to decrease the waiting time for DMEinformation. Practically all other visually read instruments aboard anair-craft provide essentially instantaneous readout information with theheretofore exception of the DME. My invention so significantly reducesthe search time of a DME that for all practical purposes, the DMEinformation has become instantaneously available to the pilot.

Another object of the invention is to provide a search mode of operationin a DME that advances the trial distance by large discrete steps to theneXt received squitter or reply pulse following the production of thelast trial distance until safe evidence of recurrent replies is detectedand the search is completed and stopped.

A further object of the invention is to provide a DME of the characterdescribed that centers the trial distance pulse (Marker) on the receivedreplies (Returns) during the search mode of operation. This featureeliminates the need for further centering when the unit switches modesfrom search to track.

A still further object of the invention is to provide a DME that isinexpensive, highly accurate and so versatile that light aircraft,medium aircraft and heavy airline type aircraft can utilize same with aminimum of conforming alterations. The advantages to each type ofaircraft is many fold and includes:

(a) Minimum of waiting time when changing channels. This becomes veryimportant during certain critical portions of aircraft operation andnavigation.

(b) Cross checking or triangulation with more than one ground stationwith a minimum of delay.

(c) Providing rapid fully automatic landing, takeoff and taxiinformation during very poor visibility conditions such as a FAAcategory III condition.

((1) In airline equipment which is computer operated, the computerremoves the DME from the operators control when such information isneeded. My invention re duces the time of computer control over the DMEto an absolute minimum and allows same to be returned to the aircraftoperator for most efficient use thereof.

(e) Due tot he almost instantaneous search characteristics of thesubject DME, a single search DME may be made to do the work of several.Accordingly, dual, or more, displays may be had from a single DME. Forexample, two indicators may represent the distance to two differentground beacons, and may be time shared with one DME. The DME would thenrapidly search and lock on one or the other of the ground beacons andalternately and successively provide information to the two indicators.

(f) Aircraft can operate safely in an air to air ranging mode with avirtually continuous display between the other aircraft and a groundstation by utilization of a single DME. In a similar manner, tailgating,e.g. flying one craft after another at the same altitude, etc., isfacilitated in long distance flights such as over oceans. A constantcheck can be made on each craft to make sure that proper distanceintervals are being maintained.

Other and further objects of the invention, together with the featuresof novelty appurtenant thereto, will appear in the course of thefollowing description.

Detailed description In the accompanying drawings which form a part ofthe specification and are to be read in conjunction therewith, and inwhich like reference numerals indicate like parts in the various views:

FIG. 1 is a block diagram showing the various important subdivisions ofthe DME;

FIG. 2 is a block diagram of the RF section of the DME showing thevoltage inputs thereto and the Megacycle and Kilocycle selector shafts;

FIG. 3 is a block diagram of the IF section;

FIG. 4 is a block diagram of the Initiation Circuit Board;

FIG. 5 is a block diagram showing both the Motor Control section and thecombination Pulse Modulator and Power Supply section;

FIG. 6 is a block diagram of the Gate Circuit Board;

FIG. 7 is a block diagram of the Operation Circuit Board and the threeRange Circuit Boards (the Mile Range Circuit Board, the One (1) MileRange Circuit Board and the Ten (10) Mile Range Circuit Board);

FIG. 8 is a plot of the search cycle waveform;

FIG. 9 is a schematic diagram of a basic binary circuit;

FIG. 10 is a schematic diagram of the basic binary circuit used in theDME with a steering network added;

FIG. 11 is a schematic diagram of the quinary counter circuit;

FIG. 12 is a partial schematic diagram of the collector circuits of thecounter shown in FIG. 11;

FIG. 13 is a circuit diagram of the quinary trigger circuit whichdirects a negative going waveform to the oil? transistor in the quinarycircuit;

FIGS. 14a and 14b are diagrams including typical voltage-current values,of a saturated and an unsaturated transistor, respectively;

FIG. 15 is a plot of the various quinary waveforms as indicated therein;

FIG. 16 is a schematic diagram of a basic Schmitt trigger circuit;

FIG. 17 is a schematic diagram of the Ten (10) Mile Range Circuit Boardshown in block diagram form in FIG. 7. It is significant to note thatthe Mile and the One (1) Mile Range Circuit Boards are identical to theTen (10) Mile Range Circuit Board;

FIG. 17a is a continuation of FIG. 17, connected as indicated, showingthe readout coils associated with the Ten (10) Mile Range Circuit Board;

FIG. 18 is a schematic diagram of the Operation Circuit Board includingthe output from the Slewing Binary, also shown in block diagram form inFIG. 7;

FIG. 19 is a view of a simulated counter register used in the shaftregister analogy;

FIG. 20 is a plot of the Trigger Waveforms showing therein typicalTrigger intervals used in the counting system;

FIG. 21 is a schematic diagram of the Initiation Circuit Board, saidCircuit Board also shown in block diagram form in FIG. 4;

FIG. 22 is a partial circuit diagram showing the and gate circuitry usedin the DME;

FIG. 23 is a schematic diagram of the Gate Circuit Board, including theSlewing Binary, said Circuit Board also shown in block diagram form inFIG. 6;

FIG. 24 is a plot of the Waveforms at critical points indicating aSubtract Error Detection;

FIG. 25 is a plot of the Waveforms at critical points rndicating a ZeroError Detection;

FIG. 26 is a plot of the Waveforms at critical points indicating an AddError Detection;

FIG. 27 is a plot of various Waveforms (including TransmitterInterrogation) at critical points during an Add Error Integration;

FIG. 28 is a diagrammatic indication of how FIGS. 27 are to berelatively arranged and interconnected;

FIG. 29 is a schematic diagram showing a basic Monostable of the typeused in the DME;

FIG. 30 is a plot of Waveforms at important points in the Monostable'shown in FIG. 29; and

FIG. 31 is a plot of various Waveforms during the search mode ofoperation.

In the description the following prefixes aid in identification of thevarious circuit components: (1) QTransistors; (2) C-Capacitors; (3)CRDiodes; (4) R-- Resistors; and (5) LInductors.

To facilitate a general discussion of the functional operation of theDME, the principal subdivisions are shown in block diagram form in FIGS.1-7. A more detailed description of these subdivisions will followinfra, however, a basic understanding of the cooperative interworkingsof the various subdivisions is necessary in order to fully appreciatethe over-all and individual inventive features disclosed hereinafter.

Of the principal subdivisions shown in FIGS. 27 (note FIG. 28 forinterconnection), the RF section, IF section, Pulse Modulator sectionand Motor Control section are disclosed in block diagram form only anddo not represent significant parts of the invention other thancooperating with the various portions of the Video section to result inthe operative unit. As a result thereof, the discussion on theabove-mentioned sections will be limited to the functional block diagramshown in FIGS. 2, 3 and 5.

The generation of the transmitted RF pulses and the conversion ofreceived RF pulses to the IF frequency of 63 mc. is accomplished by theRF unit. There are 100 different transmitter output frequencies,corresponding to VHF/VOR channels from 108.0 to 117.9 mc., which may begenerated by summing one of eleven mc. crystal frequencies and one often tenth mc. crystal frequencies in a Mixer. This Mixer outputfrequency is multiplied by a factor of twelve by Doubler V104, TriplerV103, and a Final Doubler V101 to produce the UHF frequency that will bereceived by the DME ground station (see FIG. 2).

V106A is the High Frequency Oscillator and Q101 is the Low FrequencyOscillator. Outputs from both oscillators are coupled to the MixerV106B. The plate circuit (not shown) of V106B is tuned to the mixed sumof the two oscillators. The mixed output is fed to the Amplifier V105that raises the RF power to the level required by the next stage.

All tuned circuits, involved in the above-mentioned elements of the RFsection, that change frequency with changes in channel frequency aretracked except the Low Frequency Oscillator itself. Four variableinductors (not shown) track the High Frequency Oscillator V106A, MixerV106B, Amplifier V105, and the grids of Tripler V103. The variableinductors are ganged to a Megacycle Selector shaft (represented by thebroken lines) that has eleven positions, one for each high frequencycrystal. Thus, these circuits are tracked for each change in the HighFrequency Oscillator, but not for Low Frequency Oscillator changes. Theoutput circuits of the Final Doubler V101, a portion of Tripler V103 andthe Receiver Preselector circuits are tracked by variable glasscapacitors.

DME channels are allocated so that the airborne transmitting frequencyis always 63 mc. away from the airborne receiving frequency. On DMEchannels corresponding to VOR frequencies of 108.0 to 112.2 mc., theairborne receivers frequency is below the airborne transmittersfrequency. With VOR frequencies of 112.3 to 117.9 mc., the received DMEfrequency is above the transmitted frequency. This requires that, whenchanging from a VOR frequency of 112.2 mc. to 112.3 mc., the ReceiverPreselector tuning circuits must make a jump of 137 mc. This isaccomplished by a camming arrangement that tunes the preselector glasscapacitors. The Receiver Preselector tuned circuits provide two usefulfunctions. They prevent passage of other than desired frequency signals,such as from other services operating in the UHF spectrum. They alsoprevent loss of transmitter power into the receiver, which would resultin a drop in useful transmitter output and destruction of the mixerdiode. Although both the receiver and transmitter portions of the RFunit are coupled to common antenna A, high selectivity of all the tunedcircuits precludes loss of ones energy to the other.

Since the airborne transmitter is always 63 mc. above or below thereceived frequency, depending on the particular channel in use, itconveniently follows that the same frequency transmitted qualifies foruse as local injection for a receiver mixer. This results in an IF of 63mc. RF power required for the receiver mixer is, of course, much lessthan full transmitting power. Thus, while the High Frequency OscillatorV106A and Mixer V106B run at the same power level for both functions,later stages of the transmitter run at a low level while supplying mixerinjection and then are pulsed to a much higher level during the shorttimes of RF pulse transmission.

At RF pulse transmission times, an 800 volt positive pulse of 20microsecond duration is superimposed on the DC voltages to generate thehigh RF drive level fed to the Final Doubler V101. The Final Doublerreceives plate power in the form of a pair of positive high voltagepulses of 3.5 microsecond width and 12 microsecond spacing between theirleading edges. These 1400-1 800 volt pulses are timed so as to occur atthe instant transmitted RF energy is desired. At all other times theplate voltage of V101 is zero. A small amount of RF energy at half thetransmitter output frequency is generated at V103 for receiver mixerinjection. Since V101 is also coupled to V103, a 14 volt reverse biasvoltage is present to eliminate the possibility of any RF energy beingfed through V101 and radiated during receiving. High RF drive power fromV103 during RF pulse' transmissions easily overcomes this back bias anddrives V101 into heavy conduction.

As mentioned above, antenna A is a common antenna for both the receiverand the transmitter portions of the RF section. After passing throughthe Receiver Preselector, received RF pulses from the DME ground stationare sent to a Mixer Diode CR101. Tripler V103 supplies diode CR101 withRF energy at half the required mixer injection frequency. CR101 doublesthis drive frequency and at the same time mixes the resulting doubledfrequency with signals from the Preselector. The difference frequency,63 mc., is coupled to V102, the IF Preamplifier. As Tripler V103s outputlevel is many times higher when pulsed for transmission, the drive todiode CR101 could possibly approach damaging levels. Diode CR102 isconnected in such a manner to short out the drive to diode CR101 whenTripler V103 is pulsed. A positive pulse from the Suppressor pulseoutput of the Pulse Modulator section is applied to diode CR102s anode.This reduces diode CR102s resistance to a very low value and effectivelyshorts out the high drive.

The 63 me. output from diode CR101 is amplified before leaving the RFsection by the IF Preamplifier V102. The IF section receives pairs of 63mo. pulses from the IF Preamplifier and the RF section. A single decodedvideo output pulse results for each properly coded pair of input IFpulses.

The IF section performs thre primary tasks: l) amplification of pulsesof proper frequency, (2) rejection of offfrequency pulses and (3) thegeneration of one DC output pulse for each pair of properly spacedreceived pulses. Since there is no gain in this particular receiver atthe UHF-DME channel frequencies, all receiver gain must be developed atIF frequencies.

Q301, an input transistor in the IF section, is part of an IF amplifierwith amplifies the 63 mc. pulses. The gain of Q301 is controlled by anAGC voltage (through transistor amplifiers Q311 and Q312) appliedthereto. Since frequency selectivity sufficient to reject an adjacentDME channel one megacycle away is difiicult to achieve at an IFfrequency of 63 mc., adequate rejection is realized by mixing the firstIF frequency of 63 me. with a local oscillator of 71.47 mc. to obtain asecond lower IF frequency at 8.47 mc. Tuned circuits of 8.47 mc. providethe required selectivity.

The 71.47 mc. voltage is generated by a transistor Crystal Oscillator,Q3013. The 71.47 mc. output from Q303 is applied to the emitter of Mixertransistor Q302. The 63 mc. pulses from IF Amplifier Q301 mixed with the71.47 mc. output from Q303 results in pulses of 8.47 mc., the differencefrequency, at the output of Mixer Q302. There is also a considerableconversion gain realized in Q302 with the 8.47 mc. output considerablygreater than the 63 mc. input.

